DESCRIPTION: (Verbatim from the application) Falls and fall-related injuries are the most serious, common costly medical problems facing the elderly. In the US each year there are about 30 millions falls, or about 1 per second, among 10 million fallers. In addition, of the approximately 300,000 hip fractures that occur each year, over 90% are associated with falls. We have shown previously that falls to the side with impact on the hip are associated with more than 20-fold increase in the risk of hip fractures (compared to a 3-fold increase in risk associated with reduced bone density). Thus, when screening for interventions and fracture prevention programs (pharmaceutical agents, trochanter padding or exercise), it is far less cost effective and efficient from a public health perspective to attempt to identify the 10 million elderly who will fall each year (which can now be done using relatively simple field tests) than it is to focus on the 500,000 to 600,000 elderly subjects who will fall to the side (for which comparable validated tests are not yet available). The aims of this competitive renewal application are focused on this goal. During the previous funding period, we completed the goals of Aim 1: Dynamics of Side Falls, demonstrating that slow gait speed and the postural disturbances of slipping or fainting are associated with falls to the side and impact on the hip. We have also developed the first available multi&#8209;segment, whole body model for falling and showed it to be a powerful tool for studying the biodynamics of falling to the side. For our previous Aim 2: Side Fall Risk Index, we completed both the development and refinement phases of the proposed index, demonstrating that a linear combination of tandem gait, hip abduction strength, step velocity asymmetry from the quick-step test, and sway variables while standing in a semi-tandem position could be used to distinguish elderly subjects who fell to the side from those who fell in all other directions. Under our new proposed Aim 1: Validation of Side Fall Risk Index (SFRI), we will determine whether the Side Fall Risk Index we have developed during the previous funding period can be used prospectively to identify elderly subjects who will fall to the side. As an extension of our previous work on the dynamics of side falls, under Aim 2: Gait Variability as a Predictor of Side Falls we will analyze the ground pressure time histories of elderly fallers ambulating on an instrumented mat. We will apply modern signal analysis theory to the ground pressure time histories. Using chaos theory and fractal analysis and noting that cardiovascular and neuromuscular pathologies are characterized by increased regularity of heartbeat and gait, respectively, we will determine if gait parameters determined from ground pressure time histories can be used to identify frail elderly subjects who fall to the side.